1. Field of the Invention
The invention relates to the evaluation of a corrosion inhibitor, and more particularly to a device and a method for evaluating a corrosion inhibitor for a circulating cooling water system.
2. Description of the Related Art
Typical methods for evaluating the performance of a corrosion inhibitor include an electrochemical method and a rotary coupon method.
The polarization curve method and the linear polarization resistance method, which belongs to the electrochemical method, are the most commonly used steady state electrochemical test methods. Besides, the transient test method including an AC impedance spectroscopy test has been developed and widely used. However, the current electrochemical method requires preparing a corrosive solution to be tested, such as a certain concentrated sulfuric acid solution, a hydrochloric acid solution, and a sodium chloride solution. A certain amount of the corrosive solution to be tested is then input into a three-port flask, and the corrosion of the corrosive solution to a metal is tested by using a three-electrode system in a static state. In such a system, a surface of the electrode is not washed by the water flow, but the cooling water in the circulating cooling water system flows through surfaces of a pipe and a device at a certain flow velocity and has a shearing action on the surfaces of the device and the pipe; furthermore, the solute is evenly distributed in the water. However, for electrochemical test in the laboratory, the electrode surface is not able to simulate a hydraulic condition on the surfaces of the pipe and device of the circulating cooling water system. Thus, concentration polarization easily occurs, which affects the accuracy of the testing result. Furthermore, the AC impedance spectroscopy method employs the three-electrode system and has a high requirement on the relative position of the electrodes, which causes difficulty for the installation of the three-electrode system on the circulating cooling water system.
The rotary coupon method is a common method for testing a corrosive ability. The method includes: immersing a test piece into a prepared solution for testing, rotating the solution for 72 hours; removing a rust resulting from the corrosion from the test piece, calculating a corrosion rate by a decreased weight of the test piece, and calculating a corrosion efficiency based on the corrosion rate in the presence of a corrosion inhibitor or without a corrosion inhibitor. The method is capable of directly reflecting the corrosion condition, and is very close to an actual working condition. However, the method is disadvantageous in that treatments of the test piece are necessitated before and after the corrosion, thus, errors are easily produced because of lots of human factors. Furthermore, the method is time consuming, and the testing solution reduces because of evaporation during the testing period; thus, the solution needs to replenish, which is inconvenient.
Conventional devices and methods for evaluating a corrosion inhibitor is capable of simulating the corrosion of the liquid and the condensed gas liquid on a pipe and a device at the same time, solving the problem that the pipe and the device in the industry are subject to the corrosion of both the liquid and the condensed gas liquid but the corrosion thereof are not able to be measured at the same time. The device is not capable of simulating the surface hydraulic condition in the circulating cooling water system. And the rotary coupon method requires treatments on the test piece before and after the corrosion test, thereby resulting in errors because of human factors. Besides, the improvement is desired on the capacity of simulating the hydraulic condition of the surfaces of the device and the pipeline in actual systems.